The stamping of postage stamps on envelopes can still be considered a routine postal act and was probably already so in 1864. It is uncertain why the post office in Neuötting in Upper Bavaria used red instead of the black ink that was actually prescribed.
However, because this apparently only lasted a few days, the stamps canceled in this way later became rare valuables for collectors. An envelope with such stamps has just gone under the hammer in Wiesbaden, stamped in red on June 17, 1864 in Neuötting with the then Bavarian postmark in the form of a mill wheel.
The letter actually came from Hall in Tirol to Neuötting and was addressed to the local Inn shipmaster Johann Georg Riedl, a wealthy freight forwarder who had his ships sail from Innsbruck down the Danube to Budapest. But because Riedl had just traveled to Linz, the letter was sent to him with two times six Bavarian kreuzers postage paid. This resulted in an already very rare combination of Austrian and Bavarian stamps on a single cover.
The red postmark apparently made the whole envelope worth 460,000 euros in the eyes of the now highest-bidder collector. Of course, the Neuöttinger Schiffmeister Riedl no longer has any of that. And the nameless Neuötting postal clerk with the wrong stamp color could probably be happy that the whole thing only became apparent many years later.